Restricted flow in radiant floor

I am starting up a new radiant floor system which seems to have flow restrictions in two loops. Water moves through them but very little came out when I tested it. The man who set up the manifolds said with confidence that blockage in the manifold or in the tubes was unlikely and that it must be a kink. Another man installed the tubes but he thinks it was done properly. Since the tubes are not labeled we are heating the house to see which areas don't warm. The real challenge will be to know where the kink or blockage is. Is there a way to determine this without tearing up all the gypsum board below? I plan on opening the manifold to inspect it for problems before I get too carried away. I will also flush the lines for a while. Any advice?

Thanks for the ideas. As it turns out the designer/installer misdiagnosed the problem. I took the manifold apart and found that the send flow gauges on this model (which he was not familiar with) were screwed in at different depths which affected the flow individually. This gave the impression of a blockage. There was still a lower flow through one loop but we realized that it was also a longer run with more friction loss so we adjusted the valve on each run to give a balanced flow through each. Lesson learned: check the manifold!